Pathophysiology of Heart failure

Pathophysiology of heart failure

1. HEART FAILURE
RVS CHAITANYA
KOPPALA

2. HEART FAILURE
Defined as the pathophysiologic state in which impaired cardiac
function is unable to maintain an adequate circulation for the
metabolic needs of the tissues of the body.
It may be acute or chronic.
The term congestive heart failure (CHF) is used for the chronic form
of heart failure in which the patient has evidence of congestion of
peripheral circulation and of lungs.
CHF is the end-result of various forms of serious heart diseases.

3. ETIOLOGY
Heart failure may be caused by one of the following
factors, either singly or in combination:
1. Instrinsic pump failure
2. increased workload on heart
3. impaired filling of cardiac chambers

4. 1. INTRINSIC PUMP FAILURE.
The most common and most important cause of heart failure is
weakening of the ventricular muscle due to disease so that the heart
fails to act as an efficient pump. The various diseases which may
culminate in pump failure by this mechanisms are as under:
Ischaemic heart disease
Myocarditis
Cardiomyopathies
Metabolic disorders e.g. beriberi
Disorders of the rhythm e.g. atrial fibrillation and flutter.

5. 2. INCREASED WORKLOAD ON THE HEART.
Increased mechanical load on the heart results in increased
myocardial demand resulting in myocardial failure.
Increased load on the heart may be in the form of pressure load
or volume load.
Increased pressure load
a) Systemic and pulmonary
arterial hypertension.
b) Valvular disease e.g. mitral
stenosis, aortic stenosis,
pulmonary stenosis.
c) Chronic lung diseases.
Increased volume load
a) Valvular insufficiency
b) Severe anaemia
c) Thyrotoxicosis
d) Arteriovenous shunts
e) Hypoxia due to lung
diseases.

6. 3. IMPAIRED FILLING OF CARDIAC CHAMBERS.
Decreased cardiac output and cardiac failure may result from extra-
cardiac causes or defect in filling of the heart:
Cardiac tamponade (Compression of heart) e.g. haemopericardium,
hydropericardium
Constrictive pericarditis.

7. TYPES OF HEART FAILURE
Heart failure may be
Acute or chronic
Right-sided or left sided
Forward or backward failure.
ACUTE AND CHRONIC HEART FAILURE. Depending upon whether
the heart failure develops rapidly or slowly, it may be acute or
chronic.
Acute heart failure. Sudden and rapid development of heart failure
occurs in the following conditions:
i) Larger myocardial infarction v) Acute viral myocarditis
ii) Valve rupture iv) Massive pulmonary
embolism
iii) Cardiac tamponade vi) Acute bacterial toxaemia.

8. Chronic heart failure. More often, heart failure develops
Myocardial ischaemia
Multi valvular heart disease
Systemic arterial hypertension
Chronic lung diseases resulting in hypoxia and pulmonary arterial
hypertension
Progression of acute into chronic failure.
In chronic heart failure, compensatory mechanisms like tachycardia,
cardiac dilatation and cardiac hypertrophy try to make adjustments
so as to maintain adequate cardiac output.

9. LEFT-SIDED AND RIGHT-SIDED HEART
FAILURE.
Though heart as an organ eventually fails as a whole, but
functionally, the left and right heart act as independent units.
From clinical point of view, therefore, it is helpful to consider
failure of the left and right heart separately.
The clinical manifestations of heart failure result from
accumulation of excess fluid upstream to the left or right
cardiac chamber whichever is initially affected

10. Left-sided heart failure. It is initiated by stress to the left heart. The
major causes are as follows:
Systemic hypertension
Mitral or aortic valve disease (stenosis)
Ischaemic heart disease
Myocardial diseases e.g. cardiomyopathies, myocarditis.
Restrictive pericarditis.

11. The clinical manifestations of left-sided heart failure result from
decreased left ventricular output and hence there is accumulation of
fluid upstream in the lungs.
Accordingly, the major pathologic changes are as under:
i) Pulmonary congestion and oedema causes dyspnoea and
orthopnoea
ii) Decreased left ventricular output causing hypoperfusion and
diminished oxygenation of tissues

12. Right-sided heart failure occurs more often as a consequence of
left-sided heart failure.
However, some conditions affect the right ventricle primarily,
producing right-sided heart failure. These are as follows:
i) As a consequence of left ventricular failure.
ii) Corpulmonale in which right heart failure occurs due to intrinsic
lung diseases
iii) Pulmonary or tricuspid valvular disease.
iv) Pulmonary hypertension secondary to pulmonary
thromboembolism.
v) Myocardial disease affecting right heart.
.

13. BACKWARD AND FORWARD HEART
FAILURE.
The mechanism of clinical manifestations resulting from heart failure
can be explained on the basis of mutually interdependent backward
and forward failure.
Backward heart failure. According to this concept, either of the
ventricles fails to eject blood normally, resulting in rise of end-
diastolic volume in the ventricle and increase in volume and pressure
in the atrium which is transmitted backward producing elevated
pressure in the veins.
Forward heart failure. According to this hypothesis, clinical
manifestations result directly from failure of the heart to pump blood
causing diminished flow of blood to the tissues, especially diminished
renal perfusion and activation of reninangiotensin-aldosterone
system.

14. COMPENSATORY
MECHANISMS:
CARDIAC HYPERTROPHY AND DILATATION
In order to maintain normal cardiac output, several compensatory
mechanisms play a role as under:
Compensatory enlargement in the form of cardiac hypertrophy,
cardiac dilatation, or both.
Tachycardia (i.e. increased heart rate) due to activation of
neurohumoral system e.g. release of norepinephrine and atrial
natrouretic peptide,
activation of renin-angiotensinaldosterone mechanism.

16. CARDIAC HYPERTROPHY
Hypertrophy of the heart is defined as an increase in size and
weight of the myocardium. It generally results from increased
pressure load while increased volume load (e.g. valvular
incompetence) results in hypertrophy with dilatation of the
affected chamber due to regurgitation of the blood through
incompetent valve. The atria may also undergo compensatory
changes due to increased workload.
The basic factors that stimulate the hypertrophy of the
myocardial fibres are not known. It appears that stretching of
myocardial fibres in response to stress induces the cells to
increase in length. The elongated fibres receive better nutrition
and thus increase in size. Other factors which may stimulate
increase in size of myocardial fibres are anoxia (e.g. in
coronary atherosclerosis) and influence of certain hormones
(e.g. catecholamines, pituitary growth hormone).

17. CAUSES. Hypertrophy with or without dilatation may involve
predominantly the left or the right heart, or both sides.
Left ventricular hypertrophy. The common causes are as
under:
i) Systemic hypertension
ii) Aortic stenosis and insufficiency
iii) Mitral insufficiency
iv) Coarctation of the aorta
v) Occlusive coronary artery disease
vi) Congenital anomalies like septal defects and patent ductus
arteriosus
vii) Conditions with increased cardiac output e.g. thyro-
toxicosis, anaemia, arteriovenous fistulae.

18. Right ventricular hypertrophy. Most of the causes of right
ventricular hypertrophy are due to pulmonary arterial
hypertension. These are as follows:
i) Pulmonary stenosis and insufficiency
ii) Tricuspid insufficiency
iii) Mitral stenosis and/or insufficiency
iv) Chronic lung diseases e.g. chronic emphysema,
bronchiectasis, pneumoconiosis, pulmonary vascular disease
etc.
v) Left ventricular hypertrophy and failure of the left ventricle.

19. CARDIAC DILATATION
Quite often, hypertrophy of the heart is accompanied by
cardiac dilatation. Stress leading to accumulation of excessive
volume of blood in a chamber of the heart causes increase in
length of myocardial fibres and hence cardiac dilatation as a
compensatory mechanism.

20. CAUSES. Accumulation of excessive volume of blood within
the cardiac chambers from the following causes may result in
dilatation of the respective ventricles or both:
i) Valvular insufficiency (mitral and/or aortic insufficiency
in left ventricular dilatation, tricuspid and/or pulmonary
insufficiency in right ventricular dilatation)
ii) Left-to-right shunts e.g. in VSD
iii) Conditions with high cardiac output e.g. thyrotoxicosis,
arteriovenous shunt
iv) Myocardial diseases e.g. cardiomyopathies, myocarditis
v) Systemic hypertension.